The present disclosure relates to a vent apparatus, and particularly to a vent apparatus for regulating discharge of fuel vapor from a fuel tank and admission of air into the fuel tank. More particularly, the present disclosure relates to a system for managing fuel tank vacuum conditions during purging of hydrocarbons from an emission control system coupled to the fuel tank.
Vehicle fuel systems include valves associated with a fuel tank and configured to vent pressurized or displaced fuel vapor from the vapor space in the fuel tank to a vapor recovery canister located outside of the fuel tank. The canister is designed to capture and store hydrocarbons entrained in fuel vapors that are displaced and generated in the fuel tank during a typical vehicle refueling operation or that are otherwise vented from the fuel tank.
The vapor recovery canister is also coupled to a vehicle engine and to a purge vacuum source. Typically, vacuum is applied to the vapor recovery canister by the purge vacuum source whenever the vehicle engine is running in an effort to suck hydrocarbons captured and stored in the canister into the engine for combustion.
In addition, valves associated with fuel tanks are sometimes provided with vacuum-relief valves which open in response to onset of vacuum conditions in a vehicle fuel tank. When the temperature of the vehicle fuel tank drops, the fuel vapor pressure in the vehicle fuel tank can drop to a level lower than atmospheric pressure. A vacuum-relief valve is typically configured to allow air to enter the fuel tank, thereby returning the pressure in the fuel tank to an acceptable level.